As a fuel cell, a Solid Oxide Fuel Cell (to be also referred to as SOFC), in which a solid electrolyte (solid oxide) is used, is conventionally known.
The SOFC is configured such that a number of fuel cells, having a fuel electrode and an air electrode on each surface of a solid electrolyte formed in, for example, a plate shape, is disposed so as to form a stack. The SOFC generates electricity by supplying fuel gas to the fuel electrodes, supplying air to the air electrodes, and causing a chemical reaction via the solid electrolyte between the fuel and oxygen contained in the supplied air.
For the above-described SOFC, the suitable operation temperature was previously thought to be approximately 1000° C. However, since a development has been recently made with regard to a solid electrolyte material having a low resistance, and to a type of a support membrane that enables to thinly form a solid electrolyte, the suitable operation temperature has been decreased to approximately 750° C., in which a metallic material can be used.
That is, a metallic material can be used for constituting members, except for a solid electrolyte, such as for a frame that supports a solid electrolyte, for constituting members that form a gas flow path, for an interconnector (a constituting member that obtains conduction between cells inside of a stack), and so on. By using a metallic material, having a good processing ability and a high strength, for such constituting members, highly reliable SOFCs have been able to be developed.
One common type of SOFC, in which the above-described metallic frame and the metallic interconnector are used, is a SOFC wherein plate-shaped single cells are stacked interposing interconnectors therebetween, and connected to bolts and nuts so as to form a stack (see Patent Document 1).
Moreover, an internal manifold type of SOFC has been developed wherein each of frames is provided with holes to be used as a gas flow path (a gas flow path for inflow and outflow of fuel or air), and the frames are stacked in a number of layers so as to form a gas manifold (see Patent Document 2).
Furthermore, an apparatus has been proposed wherein a gas flow path is provided at four corners of frames so as to penetrate a stack, and gas is supplied to each cell (see Patent Document 3).    Patent Document 1: Unexamined Japanese Patent Publication No. 2005-174884    Patent Document 2: Unexamined Japanese Patent Publication No. 6-349506    Patent Document 3: Unexamined Japanese Patent Publication No. 8-273691